Liquid ammonia explosion treatment of wood fibers

ABSTRACT

A process of forming improved cellulosic fibers, fibrous compositions containing cellulosic fibers, and absorbent articles comprising such compositions are disclosed. In the process, liquid ammonia penetrates cellulosic fibers in a pressurized environment, and when the pressure is released, an explosive process produces cellulosic fibers having unique structure and properties. The high pressure liquid ammonia treatment introduces a significant curl into the fiber and introduces a smooth, soft, silky feel to the fiber not present in conventional cellulosic fibers. Such fibers are particularly useful in tissue, wipes, distributive layers, fiber mats, filter papers, and other porous articles.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a Continuation-in-Part of U.S. applicationSer. No. 09/474,383, filed Dec. 29, 1999, which claims priority to U.S.Provisional Application Serial No. 60/114,373, filed on Dec. 30, 1998and assigned to Kimberly-Clark Worldwide, Inc.

FIELD OF THE INVENTION

[0002] The present invention relates to the treatment of cellulosic orwood fibers, especially after the fiber has been separated from anatural source, such as pulp or chip. The process involves treatment ofwood fibers that have had lignin reduced or eliminated therefrom ascompared to their natural condition. More specifically, the processedcellulosic or wood fibers are converted by high pressure liquid ammoniatreatment into an improved fiber, having a morphology that providesuseful properties to cellulosic web products made therefrom, such astissues, wipes, fibrous mats, filter papers and other related cellulosicfiber applications. The invention further relates to cellulosic fiberswith improved properties and absorbent article comprising such fibers.

BACKGROUND OF THE INVENTION

[0003] High-pressure treatment processes used to treat wood chips areknown. These processes basically involve rapidly moving wood chips froma high pressure environment to a lower pressure environment whereuponthe wood chips literally explode through the agency of applied physicalforces. In general, known explosion pulping processes may be classifiedinto two categories:

[0004] (1) where the defibration is produced primarily by the suddenvolatilization of a volatile liquid (normally liquid at ambienttemperature and pressure) entrapped within the interstices of the woodchips; and

[0005] (2) where the process-associated liquids are relativelynon-volatile at the operating conditions, but where the force of theexplosion is augmented by the injection of a relatively insoluble gas orgas mixture at elevated pressure.

[0006] The best known liquid explosion processes is the so called“Masonite” process, which is described in U.S. Pat. Nos. 1,655,618;1,824,221; 1,922,313; and 2,140,189. In the Masonite process, woodchipsor similar cellulosic materials are pressurized by steam at pressures ashigh as 1000 psig (6.9 MPa). Upon sudden discharge of the woodchip/water/steam mixture from the pressurizer, the water trapped withinthe interstices of the wood chips flashes to steam and provides thenecessary energy to produce a well defibrated pulp mass.

[0007] Liquid ammonia explosion treatments have also been used toconvert raw wood sources, such as wood chips. In such a process raw woodchips are impregnated with ammonia under pressure to plasticize thechips. The mixture is then exploded resulting in a material having acoarse fibrous condition that is susceptible to purification and otherprocesses. In addition, U.S. Pat. No. 5,037,663 issued to Dale,discloses treating cellulose fibers under pressure with liquid ammoniafor the purpose of improving their nutritive value or water holdingcapacity.

[0008] Wood fiber technology as understood to date provides wood fiberswith certain fibrous characteristics. The properties of cellulosic webs,fibrous mats, and other products made using the fibers often relatedirectly to various aspects of fiber morphology. Examples of such websinclude, but are not limited to webs and mats used to form papers,garments, and absorbent products. There is a need for fibers that havean increased curl and that will form bulkier webs and webs that feelsoft and silky to the touch.

[0009] A substantial need exists to produce a fiber having a highpermanent curl index and a smooth silky feel as evaluated by typicalindustry sensory test panel standards.

SUMMARY OF THE INVENTION

[0010] The present invention is directed to a process for forming animproved cellulosic fiber. The process includes the steps of: charging avessel with a composition comprising cellulosic fibrous material inwhich lignin levels have been reduced or eliminated as compared tonatural levels; charging the vessel with liquid ammonia at sufficientpressure to cause the ammonia to penetrate the cellulose fiber therebysaturating the fiber with the ammonia, and rapidly depressurizing theammonia-saturated fiber to substantially modify the fiber morphology.

[0011] The present invention is also directed to an improved cellulosicfiber formed by a liquid ammonia explosion process. The resulting fiberpossesses improved properties related to the morphology of the fiber. Inone embodiment of the invention, the resulting cellulosic fibers have acurl index of at least 0.2, and possess a smoother, softer, and moresilky feel as compared to fibers that have not been treated with ammoniaand as compared to fibers treated with gaseous ammonia only.

[0012] The present invention is further directed to cellulosic webscontaining the improved cellulosic fibers. The increased bulk, smoothsilky feel, and curl index of the improved cellulosic fibers result inthe formation of cellulosic webs having beneficial properties. Thecellulosic webs of the present invention may be incorporated into avariety of disposable absorbent products to provide improved bulk,softness and excellent ability to absorb fluids.

[0013] These and other features and advantages of the present inventionwill become apparent after a review of the following detaileddescription of the disclosed embodiments and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention relates to a high-pressure ammoniatreatment process and an improved cellulosic fiber made by the process.In the process of the present invention, ammonia penetrates both thecrystalline and amorphous portions of the fiber material. After theammonia has penetrated the fiber, pressure is released, which causesexplosion of the ammonia-filled fiber. Treatment of cellulosic fiberswith ammonia, followed by rapid decompression of the ammonia-fibersuspension, results in changes in the fibers that are related tomorphological, physical and chemical changes in the components of thefibers. The “explosive” decompression results in fibers that havepermanent fiber morphology changes, including kinks and curls, highrelative wet resilience, and a relatively high water retention value.The invention further relates to improved fibers having Wet Curl Valuesof at least about 0.2. The invention further relates to compositions,structures, and articles comprising the improved fibers.

[0015] As used herein, the term “permanent fiber morphology” is definedas a fiber characteristic, which remains after the fiber has been pulpedfor up to about 300 minutes. As used herein, the term “transient ortemporary fiber morphology” is defined as a fiber characteristic, whichdoes not remain after the fiber has been repulped for up to 150 minutes.

[0016] As used herein, the terms “purification” and “purified” inreference to any fiber or fibrous composition shall mean any processesby which the lignin content of a fibrous material has been reduced oreliminated, and fibers and fibrous compositions that have undergone suchprocesses. Examples of purification methods include, but are not limitedto, certain pulping processes. Examples of pulping processes include,but are not limited to, mechanical, chemimechanical, semichemical, andchemical processes such as kraft and sulfite processes. In someembodiments, the fibers present in the vessel and thus used in theammonia explosion process are cellulosic fibers that have been treatedby a low yield pulping process. Yield in a pulping process refers to thedry weight of fibrous material after pulping as a percentage of the dryweight of the wood material used in the pulping process. Although theterm “yield” is often considered in connection with pulping processes,the term is not intended to be limiting to such processes, and thepresent invention includes processes using fibrous materials for whichlignin content has been reduced by processes other than pulping.Further, the term “yield” may be used to describe processes other thanpulping processes. As used herein, “low yield” cellulosic fibers arefibers produced by processes that yield about 60 percent or less. Incontrast, “high yield” cellulosic fibers are those fibers produced byprocesses that yield above about 60 percent or greater. As a generalmatter, it has been found that reducing lignin content of a fibrousmaterial prior to liquid ammonia treatment will typically result in theaddition of more curl and other beneficial characteristics to the fibersthrough the treatment process. Further, in some embodiments it has beenfound that the degree of curl and other beneficial fiber characteristicsincreases as the lignin content in the fibrous material decreases. Insome embodiments, the fibers are produced by a process having a yield of55 percent or less. In other embodiments, the fibers are produced by aprocess having a yield of 50 percent or less. In other embodiments, thefibers are produced by a process having a yield of 45 percent or less.In other embodiments, the fibers are produced by a process having ayield of 40 percent or less.

[0017] Any cellulosic fibers may be employed in the process of thepresent invention. Illustrative cellulosic fibers include, but are notlimited to, wood and wood products, such as wood pulp fibers; non-woody,paper-making fibers from cotton, from straws and grasses, such as riceand esparto, from canes and reeds, such as bagasse, from bamboos, fromstalks with bast fibers, such as jute, flax, kenaf, cannabis, linen andramie; and from leaf fibers, such as abaca and sisal. It is alsopossible to use mixtures of one or more cellulosic fibers. Suitably, thecellulosic fiber used is from a wood source. Suitable wood sourcesinclude, but are not limited to, softwood sources such as pines,spruces, and firs; and hardwood sources such as oaks, eucalyptuses,poplars, beeches, and aspens. In some embodiments, fibers are mixed withother materials, including, for example, synthetic fibers and othernon-cellulosic fibers.

[0018] In some embodiments of the present invention, purified cellulosicfibers are used. After sufficient purification, the cellulosic fibersare substantially in the form of individual cellulosic fibers, althoughsuch individual cellulosic fibers may be in an aggregate form such as apulp sheet. Thus, the current process of the present invention is incontrast to known steam explosion processes that generally treatcellulosic material in the form of virgin wood chips or the like. Insome embodiments, the current process can be used as a process formodifying cellulose fibers in which lignin content has been reduced oreliminated, as compared to known steam explosion processes that aregenerally used for processing raw wood material or waste-recycleprocesses. The use of purified fibers is not intended to be limiting,however, and the invention includes treatments of wood at any stagebefore during, or after purification.

[0019] Methods of Treating Fibers

[0020] The liquid ammonia explosion treatment process of the presentinvention includes the following steps: (1) charging a vessel withcellulosic fibers, (2) charging the vessel with ammonia at sufficientpressure to cause the ammonia to penetrate the cellulose fiber, and (3)rapidly depressurizing the ammonia-saturated fiber. Although the terms“vessel” and “reaction vessel” are used throughout this application, itwill be understood that any type of vessel, container or enclosure knownto those having skill in the art or developed in the future can beemployed, as long as the vessel has sufficient capacity and is capableof withstanding the pressure of the process. As such, the terms “vessel”and “reaction vessel” are not limiting and include any such container orenclosure. Suitable vessels include, but are not limited to, reactionvessels disclosed in Canadian Patent No. 1,070,537, dated Jan. 29, 1980;Canadian Patent No. 1,070,646, dated Jan. 29, 1980; Canadian Patent No.1,119,033, dated Mar. 2, 1982; Canadian Patent No. 1,138,708, dated Jan.4, 1983; and U.S. Pat. No. 5,262,003, issued Nov. 16, 1993, all of whichare incorporated herein by reference in their entirety.

[0021] The cellulosic fibrous compositions used in the process of thepresent invention may be in either a dry or a wet state at the time ofprocessing. In one embodiment of the present invention, the cellulosicfibers are present in an aqueous mixture having a specific consistency.As used herein, the term “consistency” refers to the concentration ofcellulosic fibrous compositions in an aqueous mixture. In manyembodiments, the cellulosic fibrous composition has been dried ordewatered to reduce or to eliminate water content in the composition.Such processes reduce the opportunity for water to interfere with theprocess by causing the ammonia to form ammonium ions. In otherembodiments, the cellulosic fibers for use in the process of the presentinvention are mixed with an aqueous solution. The consistency of afiber-containing mixture is presented as a weight percent representingthe weight amount of cellulosic fibers present in an aqueous mixturedivided by the total weight amount of cellulosic fibers, water, andother components present in such mixture, multiplied by 100. In oneembodiment, the mixture has a consistency of from about 10 to about 100weight percent. In another embodiment, the mixture has a consistencyranging from about 20 to about 80 weight percent. In another embodiment,the mixture has a consistency ranging from about 25 to about 75 weightpercent cellulosic fibrous composition, based on the total weightpercent of the aqueous pulp mixture. In one embodiment, the fibrouscomposition has a consistency of about 30%. It has been found thatassuring that the aqueous mixture is agitated, stirred, or blended toeffectively disperse the cellulosic fibers throughout the water prior toits introduction into the vessel is beneficial in achieving uniformfiber treatment.

[0022] Where an aqueous composition is present, other liquids may beused in combination with water. In some embodiments, the liquid phase ofthe aqueous mixture comprises at least about 30 weight percent water. Insome embodiments, the liquid phase comprises at least about 50 weightpercent water. In some embodiments, the liquid phase comprises at leastabout 75 weight percent water. In some embodiments, the liquid phasecomprises 100 weight percent water. When another liquid is employed withthe water, such other suitable liquids include, but are not limited to,methanol, ethanol, isopropanol, acetone, and combinations thereof. Anyliquids may be used, although it is some liquids adversely affect thedispersibility of the cellulosic fibers within the mixture.

[0023] In one embodiment of the present invention, an aqueous solutiondirectly from a pulping and/or pulp preparation process is used in theammonia explosion treatment of the present invention. In thisembodiment, the amount of water and other process conditions may need tobe monitored in order to produce a suitable aqueous mixture for use inthe process of the present invention. In some embodiments, the fibrouscomposition is fiberized, for example in a hammermill, prior toprocessing. While not wanting to be bound to a particular theory, it isbelieved that fiberizing enhances the ability of ammonia to penetratethe individual fibers by exposing a greater portion of the fiber surfacearea.

[0024] Also present in the vessel is a volume of ammonia, preferablyliquid ammonia. The ammonia may be placed in the vessel before or afterthe fibrous composition, or at the same time. In some embodiments, thefibrous composition is inserted before the ammonia to assure that thefibers are immersed in ammonia. While the invention includes any rangeof weight ratios between ammonia and fibers, in some embodiments theweight ratio of ammonia to dry weight cellulosic fibrous composition inthe reaction vessel is from about 1:1 to about 8:1. In one embodiment,the ratio is from about 3:1 to about 7:1. In another embodiment, theratio is about 5:1. In some embodiments, the ammonia is charged into thevessel at sufficient pressure and temperature to maintain the ammonia ina liquid state. Any pressure effective to cause the ammonia to penetratethe fibers may be used. In some embodiments, pressure range is fromabout 100 to about 300 pounds per square inch (psi). In one embodiment,pressure is approximately 200 psi. The high-pressure forces within thevessel enables the liquid ammonia to penetrate crystalline and amorphousregions within the cellulosic fiber. The process may be performed at anytemperature.

[0025] The ammonia is allowed to penetrate the fibers. Any degree ofpenetration is included within the present invention. In someembodiments, fibers are penetrated to saturation equilibrium. In someembodiments, saturation equilibrium involves fibers containing ammoniain an amount equal to 100% of fiber dry weight or higher. In otherembodiments, the saturation equilibrium involves fibers containingammonia in an amount equal to or less than 100% of fiber dry weight.

[0026] Similarly the time duration for which the fibers are pressurizedmay be any amount. In one embodiment, the time ranges from about 0.5minutes to about 30 minutes; however, the amount of time may be shorteror longer than this duration depending on a number of factors including,but not limited to, the ammonia concentration, the pressure, and theamount of ammonia and fibers present. In some embodiments, the timenecessary to reach a saturation equilibrium condition between theammonia and the cellulosic fibers is from about 0.5 minute to about 20minutes. In other embodiments, the time necessary to reach a saturationequilibrium condition between the ammonia and the cellulosic fibers isfrom about 1 minute to about 10 minutes.

[0027] In general, the higher the volume ratio of ammonia employed, theshorter the period of time necessary to achieve a specific degree ofpenetration or saturation, and ultimately, fiber modification. As such,it may be possible to achieve essentially equivalent degrees of fibermodification for different cellulosic fiber samples by using differentcombinations of reaction conditions, such as ammonia concentrations andsaturation times.

[0028] The fibrous material is then rapidly depressurized by relievingthe pressure from the environment surrounding the ammonia/fiber mixture.Any method of pressure release can be used. In some embodiments,depressurizing involves releasing or expelling fibers from the vessel toan environment that is not pressurized, for example by releasing thefibers through an oscillating valve. In some embodiments, the vesselcontinues to maintain pressure, for example in a continuous process. Inother embodiments, depressurization involves venting the vessel. Whilenot wanting to be bound to a specific theory, it is believed that, upondepressurization, the liquid ammonia flashes into a gas, causing theammonia-saturated wood fiber to “explode” within the reaction vessel,and thereby changing the fibers morphologically, chemically andphysically due to the combination of mechanical action of the processand the chemical action resulting from the penetration of the cellulosicfibers by the ammonia. In many embodiments, the resultant fibers have aunique combination of curl as part of their permanent fiber morphology,high wet resilience and high water retention value.

[0029] The process physically changes the fiber, causing the cellulosicfibers to become modified. Without intending to be bound hereby, it isbelieved that the ammonia explosion process causes the cellulosic fibersto undergo a curling phenomenon. The cellulosic fibers, in addition tobeing modified, have been discovered to exhibit improved properties thatmake such fibers suitable for use in liquid absorption or liquidhandling applications. After the process, the treated cellulosic fibersin some embodiments will exhibit a level of curl as part of theirpermanent fiber morphology. In some embodiments, the curl is stable andwill remain as such upon exposure to water. As such, the process of theinvention generally does not require the use of any additional additivesto the cellulosic fibers during the process or any post-treatment stepsafter the process of the fibers to achieve or to retain the fiber curl.The foregoing statement is not intended to be limiting, however, andembodiments exist in which the processes involve other steps ortreatments for a variety of purposes. For example, fibers may be driedby a variety of means. Examples include, but are not limited to airdrying, oven drying, drying upon a heated surfaced, and through-airdrying. Rinsing may also be employed to remove ammonia from the fiber.Embodiments exist in which numerous other process steps and combinationsof process steps are added.

[0030] It has been found that treatments involving liquid ammoniaprovide better, more dramatic results than treatments with ammonia gas.Ammonia gas treatments generally do not provide the degree of bulkenhancement or increase in softness as treatments involving liquidammonia. Treatments with liquid ammonia generally provide fibers thatwill form a softer, more silky fibrous webs than fibers formed bytreatments with gaseous ammonia. Higher bulk generally improves wetresilience and water retention of the resulting webs.

[0031] Fibers

[0032] The present invention is further directed to improved cellulosicfibers. In some embodiments, the cellulosic fibers exhibit a stablecurl. Curl of a fiber may be quantified by a curl value, which measuresthe fractional shortening of a fiber due to kinks, twists, and/or bendsin the fiber. For the purposes of the present invention, fiber curlvalue is measured by viewing the fiber in a two dimensional plane suchas by light microscopy. To determine the curl value of a fiber, theprojected length of a fiber, corresponding to the longest dimension of atwo-dimensional rectangle encompassing the fiber, I, and the actuallength of the fiber, L, are both measured. An image analysis method maybe used to measure L and I. A suitable image analysis method isdescribed in U.S. Pat. No. 4,898,642, incorporated herein in itsentirety by reference. The curl value of a fiber may then be calculatedfrom the following equation:

Curl Value (L/I)−1

[0033] Depending on the nature of the curl of a conventionally producedcellulosic fiber, the curl may remain stable when the cellulosic fiberis dry, but may be lost in whole or in part when the cellulosic fiber iswet. The cellulosic fibers prepared according to the process of thepresent invention have been found to maintain much of their fiber curlwhen wet. This property of the cellulosic fibers may be quantified by aWet Curl value, which is simply the Curl Value when wet. Wet Curl can bemeasured according to the test method described herein or an equivalenttest method. The method disclosed herein is a mean curl average of about4000 fibers or more from a fiber sample. The Wet Curl value representsthe summation of the individual curl values for each wet fiber in thesample multiplied by the fiber's actual length, L, divided by thesummation of the actual lengths of the fibers. Wet Curl value iscalculated by using only fibers with a length of about 0.4 millimeter orgreater.

[0034] Another aspect of the invention is cellulosic fibers that exhibita curl index greater than about 0.2 and a Wet Curl value that is greaterthan about 0.2. In one embodiment, the improved cellulosic fibersexhibit a Wet Curl value of from about 0.2 to about 0.4. In anotherembodiment, the improved cellulosic fibers exhibit a Wet Curl value offrom about 0.2 to about 0.35. In another embodiment, the improvedcellulosic fibers exhibit a Wet Curl value of from about 0.22 to about0.33. In another embodiment, the improved cellulosic fibers exhibit aWet Curl value of from about 0.25 to about 0.33. In contrast, cellulosicfibers that have not been treated in accordance with the presentinvention generally exhibit a Wet Curl value that is less than about0.2.

[0035] In addition to improved Wet Curl values, the improved cellulosicfibers of the present invention exhibit a relatively high waterretention value.

[0036] The treated cellulosic fibers of the present invention aresuitable for use in a wide variety of applications. In some embodiments,depending on the use intended for the treated cellulosic fibers, thetreated cellulosic fibers are washed with water, for example, to removethe ammonia. If any additional processing procedures are planned becauseof the specific use for which the treated cellulosic fibers areintended, other well-known recovery and post-treatment steps may be usedwithout adversely affecting the properties of the cellulosic fibers.

[0037] In one embodiment, the fibers have a more soft, smooth, and silkyfeel than fibers that have not been treated with ammonia or fibers thathave been treated with gaseous ammonia only.

[0038] Absorbent Compositions, Structures, and Articles

[0039] In some embodiments of the present invention, the treatedcellulosic fibers, prepared according to the process of the presentinvention, are formed into a fibrous web for incorporation into anabsorbent structure. A fibrous web may take the form of, for example, abatt of comminuted wood pulp fluff, a tissue layer, a hydroentangledpulp sheet, a mechanically softened pulp sheet, or a nonwoven fabric. Anexemplary absorbent structure is described in copending U.S. PatentApplication Serial No. 60/008,994, which is incorporated herein in itsentirety by reference. Fibrous webs containing the improved cellulosicfibers of the present invention may be formed by an air-laying processor a wet-laid process, or by essentially any other process known tothose skilled in the art for forming a fibrous web.

[0040] The cellulosic fibers treated according to the process of thepresent invention are particularly suited for use in disposableabsorbent products such as diapers, adult incontinent products, and bedpads; catamenial devices such as sanitary napkins, and tampons; otherabsorbent products such as wipes, bibs, wound dressings, and surgicalcapes or drapes; laboratory uses such as filter papers; and tissue-basedproducts such as facial or bathroom tissues, household towels, wipes andrelated products. Accordingly, the present invention further relates todisposable absorbent products comprising the cellulosic fibers treatedaccording to the process of the present invention.

[0041] In one embodiment of the present invention, the treated fibersprepared according to the above-described process are formed into ahandsheet, such as a tissue-based product. Such a handsheet may beformed by either a wet-laid or an air-laid process. A wet-laid handsheetmay be prepared, for example, according to the method disclosed herein.It has been discovered that a wet-laid handsheet prepared from thetreated cellulosic fibers prepared according to the above-describedprocess may exhibit a density that is lower than a wet-laid handsheetprepared from cellulosic fibers that have not been treated according tothe process of the present invention.

[0042] It has also been discovered that a wet-laid handsheet preparedfrom the treated cellulosic fibers of the present invention may exhibitan increased bulk and higher absorbent capacity than a wet-laidhandsheet prepared from cellulosic fibers that have not been treatedaccording to the process of the invention.

[0043] In a further embodiment of the present invention, the treatedcellulosic fibers of the present invention are used as a component in adisposable absorbent product. The disposable absorbent product comprisesa liquid-permeable topsheet, a backsheet attached to theliquid-permeable topsheet, and an absorbent structure positioned betweenthe liquid-permeable topsheet and the backsheet, wherein the absorbentstructure comprises treated cellulosic fibers of the present invention.The structure of the disposable absorbent products may vary dependingupon the use of the final product. Exemplary disposable absorbentproducts are described in U.S. Pat. Nos. 4,710,187; 4,762,521;4,770,656; and 4,798,603; all of which are incorporated herein byreference it their entirety.

[0044] The following test methods may be used to evaluate the improvedcellulosic fibers produced from the ammonia explosion process of thepresent invention, as well as, fiber-containing webs containing suchfibers:

[0045] Wet Curl Test

[0046] The Wet Curl value for cellulosic fibers is determined by usingan instrument or method which accurately determines the Wet Curl valueof fibers. Any device or method capable of accurately determining WetCurl values of a sample may be used. One such instrument is availablefrom OPTest Equipment Inc., Hawkesbury, Ontario, Canada, under thedesignation Fiber Quality Analyzer, OpTest Product Code DA93.

[0047] To conduct the test using the foregoing instrument, a sample ofdried cellulosic fibers is obtained. The cellulosic fiber sample ispoured into a 600-milliliter plastic sample beaker to be used in theFiber Quality Analyzer. The fiber sample in the beaker is diluted withtap water until the fiber concentration in the beaker is about 10 toabout 25 fibers per second for evaluation by the Fiber Quality Analyzer.

[0048] An empty plastic sample beaker is filled with tap water andplaced in the Fiber Quality Analyzer test chamber. The <System Check>button of the Fiber Quality Analyzer is then pushed. If the plasticsample beaker filled with tap water is properly placed in the testchamber, the <OK> button of the Fiber Quality Analyzer is then pushed.The Fiber Quality Analyzer then performs a self-test. If a warning isnot displayed on the screen after the self-test, the machine is ready totest the fiber sample.

[0049] The plastic sample beaker filled with tap water is removed fromthe test chamber and replaced with the fiber sample beaker. The<Measure> button of the Fiber Quality Analyzer is then pushed. The <NewMeasurement> button of the Fiber Quality Analyzer is then pushed. Anidentification of the fiber sample is then typed into the Fiber QualityAnalyzer. The <OK> button of the Fiber Quality Analyzer is then pushed.The <Options> button of the Fiber Quality Analyzer is then pushed. Thefiber count is set at 4,000, although any higher number may be used. Theparameters of scaling of a graph to be printed out may be setautomatically or to desired values. The <Previous> button of the FiberQuality Analyzer is then pushed. The <Start> button of the Fiber QualityAnalyzer is then pushed. If the fiber sample beaker is property placedin the test chamber, the <OK> button of the Fiber Quality Analyzer isthen pushed. The Fiber Quality Analyzer then begins testing and displaysthe fibers passing through the flow cell. The Fiber Quality Analyzeralso displays the fiber frequency passing through the flow cell, whichis about 10 to about 25 fibers per second. If the fiber frequency isoutside of this range, the <Stop> button of the Fiber Quality Analyzershould be pushed and the fiber sample should be diluted or have morefibers added to bring the fiber frequency within the desired range. Ifthe fiber frequency is sufficient, the Fiber Quality Analyzer tests thefiber sample until it has reached a count of 4000 fibers, or the desirednumber, at which time the Fiber Quality Analyzer automatically stops.The <Results> button of the Fiber Quality Analyzer is then pushed. TheFiber Quality Analyzer calculates the Wet Curl value of the fibersample, which prints out by pushing the <Done> button of the FiberQuality Analyzer.

[0050] The present invention is further illustrated by the followingexamples, which are not to be construed in any way as imposinglimitations upon the scope thereof On the contrary, it is to be clearlyunderstood that resort may be had to various other embodiments,modifications, and equivalents thereof, which, after reading thedescription herein, may suggest themselves to those skilled in the artwithout departing from the spirit of the present invention.

EXAMPLES 1-4 Preparation of Improved Cellulosic Fibers of the PresentInvention

[0051] In Examples 1-4, cellulosic fiber samples were prepared bydewatering various pulp types in a laboratory centrifuge. Each Examplerefers to a different type of pulp. The four Examples include: asouthern softwood kraft pulp, available from U.S. Alliance Coosa PinesCorporation under the designation CR54 southern softwood kraft pulp(Example 1); a northern softwood kraft pulp, available fromKimberly-Clark Corporation under the designation LL-19 northern softwoodkraft pulp (Example 2); a Eucalyptus pulp, available from CeluloseNipo-Brasileira S. A. of Brazil (Example 3); and bleachedchemi-thermo-mechanical pulp (BCTMP) pulp fibers, made with northernsoftwood fibers and available from Tembec Inc. of Canada (Example 4).BCTMP fibers have significantly higher lignin contents than kraft pulps,thus providing an illustration of the relationship between lignin levelsand the efficacy of the process. Fiber samples for each of the fourexamples formed a mixture having a consistency of about 30 weightpercent cellulosic fibers, with the remaining 70 weight percent wasprimarily an aqueous liquid.

[0052] For each Example, numerous samples of about 100 grams wereprepared and treated using a variety of protocols. For each Example,different categories of samples were prepared reflecting five differenttreatment protocols. The five categories were: (A) Control; (B) Gastreated, rinsed; (C) Gas treated, unrinsed; (D) Liquid treated, rinsed;and (E) Liquid treated, unrinsed. The five treatment protocols are setforth below.

[0053] A) Treatment Protocol for Control Samples

[0054] The control sample was a dried fibrous composition, used to formhandsheets in the form as received from the supplier, without anyammonia treatment.

[0055] B) Treatment Protocol for Gas Treated, Rinsed Samples

[0056] Samples comprising approximately 100 grams fibers by dry weightwere placed in a cylindrical laboratory ammonia explosion reactoravailable from Stake Technology Ltd., Norval, Ontario, Canada. Thereactor had a capacity of 2 liters. The top valve of the reactor wasclosed such that the reactor was sealed. Gaseous ammonia was theninjected into the reactor until the internal pressure of the reactorreached about 110 psi and additional ammonia was added as necessary tomaintain the 110 psi pressure for five minutes. The cellulosic fiberswere then explosively decompressed and discharged into a container byopening the bottom valve of the reaction vessel. Prior to drying, thetreated fibers were rinsed with water until the fibers exhibited a pHbetween about 6 and about 7. Fibers were dried without rinsing.

[0057] C) Treatment Protocol for Gas Treated, Unrinsed Samples

[0058] Samples weighing approximately 100 grams were placed in alaboratory ammonia explosion reactor, available from Stake TechnologyLtd., Norval, Ontario, Canada. The reactor had a capacity of 2 liters.The top valve of the reactor was closed such that the reactor wassealed. Gaseous ammonia until the internal pressure of the reactorreached about 110 psi and additional ammonia was added as necessary tomaintain the 110 psi pressure for five minutes. The cellulosic fiberswere then explosively decompressed and discharged into a container byopening the bottom valve of the reaction vessel. Fibers were driedwithout rinsing.

[0059] D) Treatment Protocol for Liquid Treated, Rinsed Samples

[0060] Samples weighing approximately 100 grams were placed in alaboratory ammonia explosion reactor, available from Stake TechnologyLtd., Norval, Ontario, Canada. The reactor had a capacity of 2 liters.The top valve of the reactor was closed such that the reactor wassealed. 500 grams of liquid ammonia (5:1 NH₃ to fiber ratio by mass) wasthen pumped into the reactor. Inert gas (nitrogen) was then injected asneeded to attain a pressure of 200 psi. The 200 psi pressure was thenheld for five minutes. The cellulosic fibers were then explosivelydecompressed and discharged into a container by opening the bottom valveof the reaction vessel. Prior to drying, the treated fibers were rinsedwith water until the fibers exhibited a pH between about 6 and about 7.

[0061] E) Treatment Protocol for Liquid Treated, Unrinsed Dried Samples

[0062] Samples weighing approximately 100 grams were placed in alaboratory ammonia explosion reactor, available from Stake TechnologyLtd., Norval, Ontario, Canada. The reactor had a capacity of 2 liters.The top valve of the reactor was closed such that the reactor wassealed. 500 grams of liquid ammonia (5:1 NH₃ to fiber ratio by mass) wasthen pumped into the reactor. Inert gas (nitrogen) was then injected asneeded to attain as needed to attain a pressure of 200 psi. The 200 psipressure was then held for five minutes. The cellulosic fibers were thenexplosively decompressed and discharged into a container by opening thebottom valve of the reaction vessel. Fibers were then dried withoutrinsing.

[0063] Additional Testing and Results.

[0064] The fibers of Examples 1-4 were used to form handsheets. A 7.5inch by 7.5 inch handsheet was prepared using fiber samples by using an8 inch by 8 inch cast bronze wet-laid handsheet former mold, availablefrom Voith Corporation. The handsheets had a basis weight of about 60grams per square meter. The handsheets were made using 100 percentammonia exploded fibers. A British Disintegrator mixer, available fromTesting Machines, Inc., was filled with about 2 liters of distilledwater at room temperature (23° C.) and about 45.0 grams of the fibersample. The counter on the British Disintegrator was set to zero and wasturned on until the counter runs to about 1500. The contents of theBritish Disintegrator were then poured into a vessel filled with about 8liters of distilled water.

[0065] The handsheet former, having an approximate 8 inch deep chamber,was filled with tap water to about 2 inches below the top of thehandsheet former chamber. The contents of the bucket were then pouredinto the handsheet former chamber where a dedicated stirrer was thenused to mix the suspension in the handsheet former chamber. The stirrerwas moved slowly up and down 6 times to cause small vortexes, but toavoid causing large vortexes, in the square pattern of the handsheetformer. The stirrer was then removed and the suspension is drainedthrough the forming screen of the handsheet former. The handsheet formerwas then opened and two layers of blotting paper were placed on top ofthe handsheet. A roller, applying the equivalent of about 308kiloPascals of pressure per inch, was moved back and forth one alongeach side and the center of the formed handsheet. The blotting paper,with the formed handsheet attached, was then lifted off the formingscreen. Two additional sheets of blotting paper were then placed on topof the blotting paper already upon the formed handsheet and anotheradditional sheet was placed underneath the handsheet. The stackcontaining the handsheet and sheets of blotting paper was thentransferred to a hydraulic press (available from Voith Corporation) andpressed at a pressure of 75 psia for one minute. The stack was thenplaced on a table, where the blotting papers were removed. The handsheetwas then transferred, wire side up, to the polished convex surface of an8 inch by 8 inch dryer hot plate. A canvas cover was placed over theconvex surface and handsheet and was weighted down to prevent dryinginduced wrinkling. The handsheet was dried for 2 minutes and thenremoved for subsequent evaluation.

[0066] Testing was then conducted on the handsheets. The results are setforth in Tables 1-4 below. Each of the four tables corresponds to thesample (fiber type) bearing the same number. The data rows under theheading “SI CONVERTED AVERAGE TEST DATA” refer to test data expressed inappropriate units of measurement. The data rows under the heading“AVERAGE PHYSICAL TEST DATA” refer to raw data from which the SICONVERTED AVERAGE test data were calculated. All conversions of raw datawere made according to the test methods listed.

[0067] The data presented in the following tables were calculated withthe test methods provided below. References to TAPPI methods refer tomethods issued by the Technical Association of the Pulp and PaperIndustry. References to “TECHNIBRITE Manual” refer to testing accordingthe test manual accompanying the TECHNIBRITE Micro TB-1C testinginstrument, available from Technidyne Corporation, New Albany, Ind. DataTest Method Used Specific Volume TAPPI method P220-om88 Tensile IndexTAPPI method P494-om88 Tensile Energy Absorption TAPPI method P494-om88Wet Tensile Index TAPPI method P494-om88 Wet Tensile Energy AbsorptionTAPPI method P494-om88 (ISO) Brightness TECHNIBRITE Manual (ISO) OpacityTECHNIBRITE Manual Scattering Coefficient TECHNIBRITE Manual AbsorptionCoefficient TECHNIBRITE Manual L TECHNIBRITE Manual a TECHNIBRITE Manualb TECHNIBRITE Manual

[0068] TABLE 1 RESULTS FOR EXAMPLE 1 SAMPLE ID Example 1 (CR-54)TREATMENT PROTOCOL A B C D E AMMONIA TREATMENT CONTROL GAS GAS LIQUIDLIQUID RINSING n/a YES NO YES NO PFI REVOLUTIONS 0 0 0 0 0 SI CONVERTEDAVERAGE TEST DATA Specific Volume (cm{circumflex over ( )}3/g) 2.63 2.832.90 4.30 4.31 Tensile Index (Nm/g) 26.91 19.34 15.15 2.91 3.93 TensileEnergy Absorp. (J/m{circumflex over ( )}2) 27.35 13.53 7.19 0.51 0.77(Wet) Tensile Index (Nm/g) 0.92 0.68 0.63 0.20 0.23 (Wet) Tensile EnergyAbsorp. (J/m{circumflex over ( )}2) 0.42 0.42 0.50 0.14 0.15 AVERAGEPHYSICAL TEST DATA C.S. Freeness (ml) 695 775 745 775 765 Bulk (in)0.0062 0.0067 0.0068 0.0101 0.0102 Tensile (lbs) 9.15 6.58 5.15 0.991.34 Stretch (%) 2.598 1.883 1.410 0.779 0.821 Tensile Energy Absorp.(ftib/ft{circumflex over ( )}2) 1.873 0.927 0.493 0.035 0.053 (Wet)Tensile (lbs) 0.313 0.231 0.213 0.068 0.079 (Wet) Stretch (%) 1.5872.143 2.481 2.875 2.717 (Wet) Tensile Energy Absorp. (J/m{circumflexover ( )}2) 0.029 0.029 0.034 0.009 0.010 Porosity (Frazier)(cfm/ft{circumflex over ( )}2) 145.5 161.2 189.2 >747 586.1 AVERAGEOPTICAL TEST DATA (ISO) Brightness (%) 85.55 82.23 82.28 85.66 88.21(ISO) Opacity (%) 72.60 72.94 73.66 73.43 71.05 Scattering Coefficient(m²/kg) 31.49 30.51 31.45 32.73 28.12 Absorption Coefficient (m²/kg)0.21 0.27 0.28 0.21 0.26 L* (%) 95.67 94.97 94.99 95.73 94.86 a* (%)−0.60 −0.59 −0.53 −0.61 −0.52 b* (%) 2.85 4.14 4.12 2.83 3.96

[0069] TABLE 2 RESULTS FOR EXAMPLE 2 SAMPLE ID Example 2 (LL-19)TREATMENT PROTOCOL A B C D E E AMMONIA TREATMENT CONTROL GAS GAS LIQUIDLIQUID LIQUID RINSING n/a YES NO YES NO NO PFI REVOLUTIONS 0 0 0 0 0 0SI CONVERTED AVERAGE TEST DATA Specific Volume (cm³/g) 2.52 2.75 2.873.90 4.19 3.99 Tensile Index (Nm/g) 24.34 14.19 16.60 3.11 4.14 4.73Tensile Energy Absrp. (J/m²) 20.45 6.46 7.82 0.53 0.94 1.19 (Wet)Tensile Index (Nm/g) 1.06 0.86 0.81 0.26 0.30 0.35 (Wet) Tensile EnergyAbsrp. (J/m²) 0.97 0.83 0.86 0.21 0.23 0.42 AVERAGE PHYSICAL TEST DATAC.S. Freeness (ml) 685 725 695 750 730 720 Bulk (In) 0.0059 0.00650.0068 0.0092 0.0099 0.0094 Tensile (lbs.) 8.27 4.82 5.64 1.06 1.41 1.61Stretch (%) 2.197 1.377 1.409 0.803 0.897 0.947 Tensile Energy Absorp.(ftlb/ft-2) 1.401 0.442 0.536 0.036 0.064 0.081 (Wet) Tensile (lbs.)0.360 0.292 0.277 0.089 0.101 0.119 (Wet) Stretch (%) 2.608 2.793 2.9063.360 3.105 3.903 (Wet) Tensile Energy Absrp. (J/m{circumflex over( )}2) 0.067 0.057 0.059 0.015 0.016 0.028 Porosity (Frazier)(cfm/ft{circumflex over ( )}2) 78.1 163.1 141.0 470.3 489.2 452.2AVERAGE OPTICAL TEST DATA (ISO) Brightness (%) 87.88 86.80 83.60 88-0784.53 82.86 (ISO) Opacity (%) 76.00 77.35 77.60 75.82 76.85 78.91Scattering Coefficient (m{circumflex over ( )}2/kg) 38.08 39.99 38.5438.17 37.88 40.80 Absorption Coefficient (m{circumflex over ( )}2/kg)0.18 0.20 0.27 0.17 0.24 0.29 L* (%) 96.32 96.17 95.52 96.45 95.74 95.50a* (%) −0.46 −0.48 −0.47 −0.47 −0.48 −0.38 b* (%) 2.19 2.70 4.05 2.303.71 4.52

[0070] TABLE 3 RESULTS FOR EXAMPLE 3 SAMPLE ID Example 3 (EUCALYPTUS)TREATMENT PROTOCOL A B C D E AMMONIA TREATMENT CONTROL GAS GAS LIQUIDLIQUID RINSING n/a YES NO YES NO PFI REVOLUTIONS 0 0 0 0 0 SI CONVERTEDAVERAGETEST DATA Specific Volume (cm{circumflex over ( )}3/g) 2.56 2.682.82 3.63 3.77 Tensile Index (Nm/g) 16.05 15.10 11.54 4.38 4.95 TensileEnergy Absorp. (J/m{circumflex over ( )}2) 5.10 5.11 3.11 0.67 1.08(Wet) Tensile Index (Nm/g) 0.98 0.93 0.81 0.38 0.42 (Wet) Tensile EnergyAbsorp. (J/m{circumflex over ( )}2) 0.60 0.72 0.75 0.32 0.34 AVERAGEPHYSICAL TEST DATA C.S. Freeness (ml) 520 580 550 650 650 Bulk (in)0.0060 0.0063 0.0067 0.0086 0.0089 Tensile (lbs.) 5.45 5.13 3.92 1.491.68 Stretch (%) 1.072 1.132 0.964 0.701 0.864 Tensile Energy Absorp.(ftib/ft2) 0.350 0.350 0.213 0.046 0.074 (Wet) Tensile (lbs.) 0.3340.318 0.275 0.129 0.143 (Wet) Stretch (%) 2.006 2.278 2.744 3.012 2.698(Wet) Tensile Energy Absorp. (J/m{circumflex over ( )}2) 0.041 0.0490.052 0.022 0.023 Porosity (Frazier) (cfm/ft2) 81.0 101.4 95.0 411.3351.3 AVERAGE OPTICAL TEST DATA (ISO) Brightness (%) 87.85 86.65 84.2388.58 85.40 (ISO) Opacity (%) 82.70 82.73 84.27 80.48 81.77 ScatteringCoefficient (m2/kg) 54.61 53.46 55.42 48.99 49.16 Absorption Coefficient(m2/kg) 0.20 0.23 0.31 0.17 0.26 L* (%) 96.75 96.51 96.00 96.83 96.12 a*(%) −0.43 −0.43 −0.37 −0.40 −0.30 b* (%) 2.99 3.45 4.35 2.54 3.69

[0071] TABLE 4 RESULTS FOR EXAMPLE 4 SAMPLE ID Example 4 (BCTMP)TREATMENT PROTOCOL A B C D E AMMONIA TREATMENT CONTROL GAS GAS LIQUIDLIQUID RINSING n/a YES NO YES NO PFI REVOLUTIONS 0 0 0 0 0 SI CONVERTEDAVERAGE TEST DATA Specific Volume (cm{circumflex over ( )}3/g) 3.91 4.913.84 5.84 4.65 Tensile Index (Nm/g) 28.74 15.44 30.39 6.31 14.74 TensileEnergy Absorp. (J/m{circumflex over ( )}2) 17.45 5.84 18.73 2.24 7.29(Wet) Tensile Index (Nm/g) 1.00 0.67 1.27 0.38 0.48 (Wet) Tensile EnergyAbsorp. (J/m{circumflex over ( )}2) 0.23 0.20 0.32 0.20 0.38 AVERAGEPHYSICAL TEST DATA C.S. Freeness (ml) 570 730 600 745 695 Bulk (in)0.0092 0.0116 0.0091 0.0138 0.0110 Tensile (lbs.) 9.77 5.25 10.33 2.155.01 Stretch (%) 1.782 1.240 1.821 1.198 1.530 Tensile Energy Absorp.(ftib/ft{circumflex over ( )}2) 1.195 0.400 1.283 0.153 0.499 (Wet)Tensile (lbs.) 0.340 0.228 0.433 0.129 0.165 (Wet) Stretch (%) 0.8651.080 0.975 1.777 2.147 (Wet) Tensile Energy Absorp. (J/m{circumflexover ( )}2) 0.016 0.014 0.022 0.014 0.026 Porosity (Frazier)(cfm/ft{circumflex over ( )}2) 138.2 614.1 125.5 >747 399.5 AVERAGEOPTICAL TEST DATA (ISO) Brightness (%) 74.32 53.22 53.41 53.40 59.89(ISO) Opacity (%) 78.40 86.32 87.02 84.42 84.59 Scattering Coefficient(m{circumflex over ( )}2/kg) 36.76 33.36 35.52 30.27 36.09 AbsorptionCoefficient (m{circumflex over ( )}2/kg) 0.41 2.06 2.00 1.95 1.35 L* (%)94.37 87.23 87.77 86.97 89.91 a* (%) −1.85 −0.01 −0-22 0.07 −0.80 b* (%)9.91 16.58 17.30 16.01 14.71

[0072] The above specification, examples and data provide a completedescription of the manufacture and use of the composition of theinvention. Since many embodiments of the invention can be made withoutdeparting from the spirit and scope of the invention, the inventionresides in the claims hereinafter appended.

What is claimed is:
 1. A process comprising: providing a cellulosicfibrous material, said fibrous material having been processed such thatthe lignin content has been reduced therein; charging a vessel with acomposition comprising said cellulosic fibrous material; charging thevessel with ammonia at a pressure sufficient to cause the ammonia topenetrate cellulosic fibers in the cellulosic fibrous material; andrapidly depressurizing the fibrous material.
 2. The process of claim 1,wherein the vessel is charged with ammonia at a pressure sufficient tocause the ammonia to penetrate crystalline and amorphous portions of atleast some cellulosic fibers.
 3. The process of claim 1, wherein, aftercharging the vessel with ammonia, the ammonia and fibrous material areretained in the vessel for a period of time ranging from about 0.5 toabout 30 minutes.
 4. The process of claim 1, wherein the ammonia andcellulosic fibrous material are present in a weight ratio of ammonia tocellulosic fibrous material of from about 1:1 to about 8:1.
 5. Theprocess of claim 1, wherein the cellulosic fibrous material is in anaqueous mixture prior to saturation with ammonia.
 6. The process ofclaim 5, wherein the aqueous mixture comprises about 10 to about 80weight percent fibers.
 7. The process of claim 1, wherein the pressureranges from about 100 to about 300 psi.
 8. The process of claim 1,wherein the lignin content in the cellulosic fibrous material has beeneliminated through a pulping process.
 9. A cellulosic fiber madeaccording to the process of claim
 1. 10. A disposable absorbent productcomprising the fiber of claim
 9. 11. A cellulosic fiber having a curlindex of greater than 0.2; and a Wet Curl Value of at least 0.2.
 12. Thefiber of claim 11, wherein the fiber has a curl index from about 0.2 toabout 0.4.
 13. The fiber of claim 11, wherein the fiber is formed fromwood, cotton, straw, grass, cane, reed, bamboo, stalks with bast fibers,leaf fibers or a combination thereof.
 14. The fiber of claim 13, whereinthe fiber comprises wood.
 15. A fiber-containing web or fabriccomprising the fiber of claim
 11. 16. A disposable absorbent productcomprising the fiber of claim
 11. 17. A disposable absorbent productcomprising a cellulosic fiber, wherein the fiber has a curl index ofgreater than 0.2.
 18. The disposable absorbent product of claim 17,wherein the fiber has a curl index from about 0.2 to about 0.4.
 19. Thedisposable absorbent product of claim 17, wherein the product is adiaper, adult incontinent product, bed pad, catamenial device, wounddressing, surgical cape, surgical drape or tissue-based product.
 20. Thedisposable absorbent product of claim 17, wherein the product is ahandsheet.
 21. The disposable absorbent product of claim 17, wherein theproduct comprises: a topsheet; a backsheet; and an absorbent structurepositioned between the topsheet and the backsheet, wherein the absorbentstructure comprises said fiber.